Zhuanfang Zhang

Tuning the dimension of POM-based inorganic–organic hybrids from 3D self-penetrating framework to 1D poly-pendant chain via changing POM clusters and introducing secondary spacers

Through tuning the different polyoxometalate (POM) clusters and the secondary spacers, four new various dimensionality inorganic–organic hybrid compounds Cu5(pzta)6(H2O)2[Mo8O26] (1), Cu5(pzta)6(H2O)6[PW12O40]·(OH) (2), Cu4(pzta)2(bipy)(H2O)4(OH)2[Mo8O26]·2H2O (3) and [Cu2(pzta)2(bipy)2(H2O)2][HPW12O40]·8H2O (4) (pzta = 5-(2-pyrazinyl)tetrazole, bipy = 4,4′-bipyridine) have been synthesized under identical hydrothermal conditions. The four compounds were assembled from copper cations, N-donor ligands and POM clusters. Compound 1 displays a novel self-penetrating 3D framework. When the POM clusters were changed from β-[Mo8O26]4− (β-Mo8) to [PW12O40]3− (PW12), compound 2 was obtained, which is a 2D layer with square channels into which the tetradentate PW12 anions as templates are incorporated. Furthermore, by introducing second spacer bipy into the reaction system of 1 and 2, respectively, compounds 3 and 4 were obtained. 3 shows a 2D layer that consists of adjacent metal–organic chains fused together by six-connected β-Mo8 anions, and 4 exhibits a 1D poly-pendant chain constructed by dinuclear copper complexes and PW12 clusters. The distinct structural features of the four compounds suggest that different POM clusters and secondary spacers should have great effect on the structures of POM-based inorganic–organic hybrids. Additionally, the luminescent and electrochemical properties for 1–4 have been investigated.

A new 3D framework based on reduced Wells-Dawson arsenotungstates as eight-connected linkages

A new hybrid compound based on reduced Wells-Dawson arsenotungstates as eight-connected linkages, [Cu4(btb)6(H2O)2][As2WV2WVI16O62]·10H2O (1) (btb = 1,4-bis(1,2,4-triazol-1-y1)butane) has been synthesized under hydrothermal conditions. Structural analysis shows that 1 displays a 3D POMOF structure consisting of two crystal distinct motifs: a 3D MOF architecture and an eight-connected As2W18 cluster. It is worth mentioning that the 3D MOF architecture possesses two kinds of channels (A and B). The eight-connected As2W18 clusters as guests occupy the B channels and are incorporated within the MOF to achieve a 3D POMOF architecture with a novel (32·42·52)(33·45·53·64)2(36·49·59·64) topology. In addition, the electrochemical studies show that 1 has good electrocatalytic activities toward reduction of both hydrogen peroxide and nitrite molecules ascribed to W-centers. The photocatalytic properties of 1 indicate that the title compound presents a good degradation activity and may be a potential photocatalyst for oxidative decomposition of methylene blue dye.

Two novel zipper-like compounds of the usual and bivanadyl capped Keggin clusters connected by propeller-shaped complexes

By choosing asymmetric L ligands (L = 1-(imidazol-1-yl)-4-(1,2,4-triazol-1-ylmethyl)benzene), Cu2+/Co2+ cations and Keggin clusters as starting materials, two new POM-based zipper-like compounds, {Cu(L)4[HPMo12O40]}·4H2O (1) and {[Co(L)4][HPMo8VV4O40(VIVO)2]} (2), have been hydrothermally synthesized and characterized by elemental analyses, single-crystal X-ray diffraction, XPS, powder X-ray diffraction, IR spectroscopy, and TG analyses. A structural feature of 1 and 2 is that there exists a 1D + 1D → 3D interdigitated architecture achieved using molecular zippers, in which overhanging mono-coordinated L arms act as teeth. Compound 2 shows bifunctional electrocatalytic activities toward not only reduction of normal iodated inorganic molecules (IO3−) ascribed to Mo-centers, but also oxidation of biological molecules such as ascorbic acid (AA) ascribed to V-centers.

Selective electrochemical detection of dopamine in the presence of uric acid and ascorbic acid based on a composite film modified electrode

An electrochemical sensor was built by the layer-by-layer self-assembly method for selective and sensitive determination of dopamine (DA) in the presence of uric acid (UA) and ascorbic acid (AA), based on vanadium-substituted polyoxometalates, copper oxide and chitosan–palladium. This sensor was characterized by UV-vis spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry, electrochemical impedance spectroscopy and current–time were employed to investigate the electrochemical and sensing properties. The results indicated the proposed sensor had good electrocatalytic activity towards the oxidation of dopamine and exhibited a low detection limit of 0.045 μM (S/N = 3), a wide linear range of 0.25–217 μM and fast response (<2 s). In addition, the sensor exhibited excellent reproducibility, long-term stability and good anti-interference ability towards common coexistent compounds. Finally, this sensor was employed to detect DA in real blood serum samples and the recovery is acceptable within the allowed error range.

Modulating the polyoxometalate-based inorganic–organic hybrids from simple chains to complicated frameworks via changing POM clusters

Investigation into a hydrothermal reaction system with a copper salt, 1-(imidazo-1-ly)-4-(1,2,4-triazol-1-ylmethyl)benzene) (itb) ligand and three types of polyoxometalates (POMs) led to the preparation of three new coordination polymers, [Cu2(itb)4(H4P2W18O62)]·H2O (1), [Cu(itb)4(HPW12O40)]·4H2O (2) and [Cu2(itb)2(Mo8O26)]·6H2O (3). The three coordination polymers were characterized by elemental analyses, single-crystal X-ray diffraction, powder X-ray diffraction, XPS and IR spectra. Structural analyses show that with modulating the type of POM anions from [Mo8O26]4− and [PW12O40]3− to [P2W18O62]6−, the three coordination polymers possess distinct structural motifs: simple one-dimensional (1D) chain (1), 1D + 1D → 2D interdigitated architectures (2) and complicated 3D frameworks consisting of both meso-helixes and left/right-helixes (3). The distinct structural features of the three coordination polymers suggest that the POM anions should play a significant role in the process of assembly. The electrocatalytic and luminescent properties for coordination polymers 1–3 have been investigated.

The factors affecting the assembly of Keggin–metal–bimb systems: charge/polarity of Keggin polyanions and coordination modes of metal cations

To explore the influence of the charge/polarity of Keggin polyanions and coordination modes of transition metal cations on the construction of polyoxometalate (POM)-based hybrid compounds, we design two synthetic routes and obtain six new POM-based inorganic–organic hybrid compounds, namely, [Co5(H2O)6(bimb)8(PWVI10WV2O40)2]·14H2O (1), [Co2(bimb)2(GeW12O40)][bimb]·2H2O (2), [Co2(bimb)2(BW12O40)][Hbimb]·2H2O (3), [Co2(bimb)2(H2W12O40)][H2bimb]·2H2O (4), [Cu(bimb)(BW12O40)][H2bimb]2·2H2O (5) and [Ag2(bimb)2(BW12O40)][H3bimb]·2H2O (6) (bimb = 1,4-bis(1-imidazolyl)benzene). All compounds were characterized by elemental analyses, IR spectroscopy, powder X-ray diffraction and single-crystal X-ray diffraction. Compound 1 represents the first POM-based three-dimensional (3D) self-penetrating structure composed of a unique metal–organic polycatenated framework and tridentate Keggin clusters. Compounds 2, 3, 4 and 6 are isostructural, which show POMOF structures consisting of Keggin cluster guests and a metal–organic nanotube host. The structure of compound 5 is a simple 2D grid layer. The isolation of the title compounds is very informative for systematically understanding the effect of the charge/polarity of POMs and coordination modes of transition metal cations on the structures of POM-based hybrids. The effect of the charge/polarity of POMs and coordination modes of transition metal cations is discussed in this work. Additionally, the luminescence and electrochemical properties of 1–6 have been investigated in detail.

A novel Cu12(pz)12 loop-based coordination polymer templated by double-Keggin anions

A compound, [CuI5(pz)6(H2O)4][PWVI10WV2O40] (1) (pz = pyrazine), with a novel Cu12(pz)12 loop-based coordination polymer templated by double-Keggin anions, has been hydrothermally synthesized, and its photocatalytic activity has also been investigated. The results indicate that the title compound exhibits good photocatalytic activity towards degradation of rhodamine B dye and could be a potential photocatalyst for decomposition of rhodamine B dye.

Assembly of two new polyoxometalate-templated supramolecular compounds by utilizing flexible 1,4-bis(pyrazol-1-ylmethyl)benzene ligand

Two new polyoxometalate-templated supramolecular compounds, [CuI4(bpmb)4][PMoVI11MoVO40] (1) and [CuI4(bpmb)4SiW12O40] (2) (bpmb = 1,4-bis(pyrazol-1-ylmethyl)benzene), have been synthesized under hydrothermal conditions and characterized by routine methods. Structural analysis shows that in 1, there exist crown-like [CuI4(bpmb)4] coordination macrocycles, and the Keggin polyanions [PMo VI11MoVO40]4− (abbr. as PMo12), which direct the crown-like macrocycle to form a 3-D supramolecular framework. In 2, there exist unusual meso-helix chains, and these chains are mutually interlaced in a wave–trough pattern, but without intersection resulting in a multi-cavity layer, in which the [SiW12O40]4− (abbr. as SiW12) clusters as guest molecules occupy the cavities of the layers. The distinct structural features of the two compounds suggest that Keggin polyanions should play a significant role in the process of assembly. Electrocatalytic properties of 1 and 2 were investigated. Graphical Abstract Two new POM-templated supramolecular compounds with good electrocatalytic activities toward reduction of iodate have been obtained, which shows that Keggin anions should play a significant role in the process of assembly.

A molecular crown analogue templated by Keggin polyanions: synthesis, structure, and electrochemical and luminescent properties

Abstract A hybrid compound, [CuI4(bpmb)4][PWVI11WVO40] (1) (bpmb = 1,4-bis(pyrazol-1-ylmethyl)benzene), has been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction analysis, infrared spectroscopy, elemental analyses and powder X-ray diffraction. In compound 1 crown-like [Cu4(bpmb)4]4+ macrocycles templated by Keggin-type [PWVI11WVO40]4− polyanions (abbreviated PW12) exist. Supramolecular layers are formed by intermolecular hydrogen bonding interactions of discrete crown-like [Cu4(bpmb)4]4+ macrocycles and [PWVI11WVO40]4− polyanions. The electrochemical and luminescence properties of compound 1 were investigated.